Image-forming production systems, such as electrophotographic printers, are used to transfer images onto a plurality of sheets of paper or other medium. In a typical image-forming job, the image-forming production system transfers or prints one or more images onto one or more sheets. When multiple images are transferred, the image-forming process usually transfers the images to arrange the output sheets according to the image-forming job. The output sheet sequence typically corresponds to the image input sequence into the image-forming production system. This ordered input and corresponding output-avoids the need to reassemble or otherwise compile the sheets.
Many image-forming production systems, such as electrophotographic printers, have a marking engine, an inserter, and a finisher device. The marking engine transfers images onto the sheets. If required by the image-forming job, the inserter inserts a preprinted or blank sheet into the sheet output from the marking engine. The finisher device collects the output sheets to complete the image-forming job or prepare it for subsequent processing operations. In some image-forming jobs there may be a need to combine or merge imprinted sheets from the marking engine with plain sheets or sheets that do not require imaging. For such printing jobs, an insert supply or an inserted sheet may be placed downstream of the marking engine, between the marking engine and other output accessories from an inserter. There are image-production systems that are capable of combining the plain sheets from the inserter with the imprinted sheets. For the reasons which follow, the speed of sheets exiting from the marking engine may not match the output speed of the inserter. Additionally, the speed at which sheets are supplied to the inserter may be faster than the speed at which output devices can accept sheets. In more detail, in an electrophotographic marking engine, it is desirable to minimize the speed at which an image is processed and fused for a given throughput rate. The speed is minimized by positioning the sheets relatively close to each other in the feed direction on the image loop. However, for high speed inserters, vacuum feeding from supply trays to the inserter is generally preferred due to its superior reliability and performance. For maximum performance, the vacuum devices feeding the inserter require a significant time between sheets in order to safely acquire a sheet with vacuum prior to feeding. To maximize the time between sheets, the sheets are fed to the inserter at a high speed, leaving more time between feeds to acquire the next sheet. Since the sheets being fed to the inserter will be merged, in appropriate places, between sheets from the marking engine, the lower speed requirements of the marking engine are at conflict with the higher speed requirement of the inserter vacuum feed system. Merging sheets traveling at two different speeds present obvious problems.
Additionally, the high feeding speed for the inserter may be problematic for output accessories. Some output accessories or devices, such as devices that perform stacking, stapling or folding require a relatively large amount of time to accomplish these functions. Therefore, the input speed to these devices conflicts with the high speed vacuum feed speed of the inserter.
Further, some output devices such as hole punchers require as much uniformity between sheets as possible. For these devices, it is important to make the leading edge timing of sheets exiting the inserter as uniform as possible.
Accordingly, there is a need for an image-production system that is able to combine sheets from different parts of the image-production systems for a high-speed image forming job, where the merging of sheets occur at a time that is coordinated with the timing of the marking engine. There is also a need to have output devices receive sheets with uniform timing.